1. Field of the Invention
The present invention relates to a fatigue testing device for thin plates and to a fatigue test method for the same, and specifically relates to a fatigue test technique in which the fatigue test can be reliably performed.
2. Description of the Related Art
Thin plates which form metal diaphragms and metal gaskets must have sufficient elasticity and flexibility against pressure and temperature, and must maintain necessary seal against pressure in order to prevent leakage at joined surfaces. Therefore, excellent fatigue characteristics are required in these thin plates. It is important to perform fatigue tests for the thin plates forming metal diaphragms to verify fatigue characteristics when metal diaphragms are produced.
As examples of fatigue tests for thin plates proposed heretofore, there are the “Plane bending fatigue test method for metallic plate” according to JIS Z 2275 and “Fatigue test method and fatigue test device using resonance” described in Japanese Patent Unexamined (KOKAI) Publication No. 8-54331, etc.
In the above-mentioned plane bending fatigue test method for metallic plates, bending moment is set to perform the fatigue test. In this method, the bending moment must be extremely small when the thickness of a test piece is extremely thin, for example 0.5 mm or less, or else the fatigue test cannot be performed. In the test, both ends of the test piece are bent by providing moment with a mechanical structure, so that the cycle frequency is very low, for example, about 50 Hz. Therefore, the fatigue test requires 20 days or more in a case of an ultra-high cycle, for example, 108 or more, and the fatigue test cannot be performed quickly.
In contrast, “Fatigue test method and fatigue test device using resonance” described in Japanese Patent Unexamined (KOKAI) Publication No. 8-54331 is a technique in which the above-mentioned disadvantages in the technology are overcome. That is to say, in this technique, the fatigue test can also be performed on ultrathin plates and a quick fatigue test is realized with application of the resonance. However, in the technique, reliable fatigue tests cannot be performed since control of amplitude is difficult due to energy absorption by resonance in which a part of the energy generated by a vibration source is absorbed in the test piece. In particular, it is more difficult to resonate the test piece reliably when the frequency is high and the amplitude is low. Therefore, the reliability is extremely reduced in the case in which a fatigue test at high frequency is performed.